The field of art to which this invention pertains is polysaccharide derivatives.
Polygalactomannans and their derivatives are well known compositions which have many uses as thickening agents in aqueous systems.
The polygalactomannans are polysaccharides composed principally of galactose and mannose units and are usually found in the endosperm of leguminous seeds, such as guar, locust bean, honey locust, flame tree and the like. Guar gum, for example, is composed mostly of a galactomannan which essentially is a straight chain mannan with single membered galactose branches. The ratio of galctose to mannose in the guar polymer is 1:2.
Locust bean gum is a polygalactomannan gum of similar molecular structure in which the ratio of galactose to mannose is 1:4. Guar and locust bean gums are the preferred sources of the polygalactomannans, principally because of their commercial availability.
Hydroxyalkyl galactomannan gums are made by reacting the gums, such as guar gum and locust bean gum, with an alkylene oxide having at least two and, preferably, three or more carbon atoms as disclosed in U.S. Pat. No. 3,483,121. Galactomannan gums, as stated hereinabove, are composed of units of galactose and mannose sugars, each having an average of three reactive hydroxyl groups. These react with alkylene oxides to produce a hydroxyalkyl ether of the gum. Each unit of alkylene oxide added to the galactomannan gum in turn adds a new hydroxyl group which is itself reactive. Theoretically, there is no limit to the amount of alkylene oxide which may be added to the galactomannan gums. As a practical matter, however, a molecular substitution (M.S.) of about 4 to 5 is a practical upper limit.
Esters of hydroxyalkyl ethers of polygalactomannans are described in U.S. Pat. No. 2,523,708.
Mixed derivatives of polygalactomannans, i.e., carboxyalkyl hydroxyalkyl derivatives, are described in U.S. Pat. No. 3,723,409.
Modified nonionic cellulose ethers are disclosed in U.S. Pat. No. 4,228,277. The cellulose ethers described in this patent are nonionic cellulose ethers having a sufficient degree of nonionic substitution selected from the group consisting of methyl, hydroxyethyl and hydroxypropyl to cause them to be water-soluble and which then are further substituted with a hydrocarbon radical having about 10 to 24 carbon atoms in an amount between about 0.2 weight percent and the amount which renders said cellulose ethers less than 1 percent by weight soluble in water.